1. Field of the Invention
The present invention relates to reciprocating powered pumps, and more particularly to reciprocating pumps which are provided with means for adjusting the positive displacement stroke of the pump.
2. Description of the Prior Art
Adjustable stoke positive displacement pumps are known. Some such pumps are provided with eccentric reciprocating drives. The piston or chamber is driven in the feed or displacement direction against the fluid head at the outlet and also against a return spring. When the drive for the piston attempts the return stroke the positive coupling is disconnected and the piston or chamber is returned to a predetermined limited position by the return spring.
Positive displacement pumps of the prior art types load the pump motor with the work of performing the feed stroke at the same time energy is stored in the return spring for performing the suction or intake stroke.
Heretofore, positive displacement pumps have been designed and manufactured as integral assemblies. When such pumps are employed for metering pumps and the capacity limit of the pump is reached, the user has been forced to buy the next larger size pump.
Heretofore, a purchaser of a positive displacement metering pump has been limited in the accuracy available to a percentage of the maximum volume displacement of the pump being employed. Pumps employing large diameter chambers or pistons are limited in the accuracy of the adjustable stroke and as the volume being pumped is decreased the volume error remains constant regardless of the amount being pumped during each displacement stroke.
Heretofore, positive displacement pumps, especially those designed for metering chemicals, have employed check valves in the inlet lines and outlet lines which were connected through plenums to the piston or expandable chamber. Spring loaded valves of the prior art type are subject to deterioration of the valve materials. If metal springs are used the springs tend to deteriorate. If the springs are made very strong to resist deterioration and weakening, they tend to create wire drawing and or cavitation which causes errosion of the valve face and valve seats. Plastic pumps having moving pistons and concentric mating valves and seats tend to wear and or erode and are not suitable for metering pumps because leaks destroy the accuracy of the pump and its intended purpose.
Heretofore, pumps have been made from plastics which resist wear and chemical action, however such pumps have not been made in a manner which permits ease of replacement of all of the wearing parts, moving parts and parts subject to field replacement.
There is an unfullfilled need for a cheap reliable and accurate positive displacement metering pump which is resistant to most chemicals.